KR101048197B1 - LED driving circuit - Google Patents

Abstract

LED drive circuit of the present invention, LED string; A DC-AC converter for converting DC power into AC power; A transformer unit configured to transfer the converted AC power; A rectifier for rectifying the AC power received from the transformer and supplying the rectified AC power to the LED strings; And a controller for controlling the operation of the DC-AC converter according to a burst dimming signal applied from the outside.

LED driving circuit, DC-AC conversion, light emitting diode, backlight

Description

LED driving circuit {LED Driving Circuit}

The present invention relates to an LED driving circuit for supplying driving power to LEDs (Light Emitting Diodes).

LED light source devices consisting of a plurality of strings of light emitting diodes (LEDs) are rapidly spreading for a wide range of applications for lighting applications or backlights of LDC panels.

LEDs with high brightness as a whole can be used in many applications, including backlights of liquid crystal displays (LCDs) based on monitors and televisions (collectively referred to as monitors hereinafter). In large LCD monitors, LEDs are typically supplied to one or more strings of LEDs connected in series to share a common current.

To provide backlight for LCD monitors, one of two basic techniques is commonly used. The first technique uses one or more strings of white LEDs, which typically include blue LEDs with phosphors (materials). This phosphor absorbs the blue light generated by the LED and emits white light. In the second technique, one or more individual strings of colored LEDs are placed adjacent to each other so that the light combined with each other looks like white light.

Due to variations in the characteristics (eg forward voltage drop) between the LED elements of the LED string, LED strings of the same type of LEDs also exhibit different electrical characteristics (eg voltage drop). Therefore, in order to allow the same current to flow through each of the LED strings, there is a further need for controllable constant current control means or the like connected in series to each LED string to compensate for different voltage drops.

Recent LED driving circuits require a burst dimming control function, and when the constant current control means further includes a means for burst dimming control, a problem of increased manufacturing cost and / or insufficient implementation space occurs.

An object of the present invention is to provide an LED driving circuit capable of achieving a burst dimming control function in a low cost and / or a small space.

LED driving circuit according to an embodiment of the present invention, the LED string; A DC-AC converter for converting DC power into AC power; A transformer unit configured to transfer the converted AC power; A rectifier for rectifying the AC power received from the transformer and supplying the rectified AC power to the LED strings; And a controller for controlling the operation of the DC-AC converter according to a burst dimming signal applied from the outside.

By implementing the LED drive circuit of the present invention according to the above configuration, there is an advantage that the burst dimming control can be achieved in a low cost or a narrow space.

1 shows a structure of an LED driving circuit for smoothing the driving power of LED strings in a linear driving manner.

As shown, each LED string is supplied with driving power from a common power supply 11, and the bipolar transistor 13 and the op amp 12 are fixed in the current path formed by each of the LED strings 14. Current sources 19 are connected. In the illustrated circuit, the same current is supplied to each of the LED strings by the fixed current sources 19, so that the luminance of each of the LED strings 14 can be kept uniform even when there is a slight characteristic variation between the LED strings. have.

While the LED driving circuit of the illustrated method has the advantage of accurate current control and easy implementation of additional functions such as dimming, LED strings having different forward voltage drop values are unilaterally identical. By forcing a current of magnitude to flow, there is a disadvantage in that heat generation loss caused by the resistive component 16 on the current path occurs.

2 illustrates a structure of an LED driving circuit for smoothing driving power of LED strings in a switching manner.

Each of the LED strings 24 of the illustrated LED driving circuit has switching driving DC-DC converters 21, respectively. As shown in the figure, time-sharing control of the switching transistor 32 of each DC-DC converter 21 according to the current detected by the switching control IC 31 sensing the output current of each LED string, the corresponding LED string 24 Adjust the average current flowing to).

While the LED driving circuit of the illustrated method has an advantage of suppressing heat loss due to a resistive component, an accurate current control process is relatively complicated, costs are increased, and additional functions are difficult to implement.

3 is a block diagram showing the concept of the LED drive circuit of the AC conversion drive method.

The illustrated LED drive circuit includes at least two LED strings 103; A rectifier 107 for rectifying an AC voltage to supply the LED strings; A DC-AC converter 101 for converting a DC voltage into an AC voltage together with the DC power supply 11 on the power supply side; And a transformer unit 102 transferring the converted AC voltage to the rectifying unit 107.

Since the illustrated LED driving circuit drives the LED by an intermediate conversion to an alternating current, there is an advantage in that the voltage level is easily controlled and the smoothing effect of the average current by the transformer is provided. Additional objects can be achieved.

4 illustrates an LED driving circuit according to an embodiment of the present invention.

Burst Dimming is a technique that controls the brightness of cold cathode fluorescent lamps (CCFLs) by turning the lamps on and off at a faster rate than humans can visually detect. The on / off rate is usually 100Hz to 300Hz. The higher the ratio of on time-off time, the brighter the light source device. The optimum range of the on time-off time ratio may be determined according to the reaction speed of the light source element constituting the light source device.

The illustrated LED driving circuit includes at least two LED strings 132 and 134; A DC-AC converter for converting DC power into AC power; A transformer unit 120 for transferring the converted AC power; A rectifier for rectifying AC power received from the transformer unit 120 and supplying the rectified AC power to the LED strings 132 and 134; And a controller for controlling the operation of the DC-AC converter according to a burst dimming signal applied from the outside.

The DC-AC converter may include switching elements 112 and 114 that are switched according to an alternating frequency to be converted.

The LED driving circuit may further include a sensing resistor 192 as a current detecting means for detecting a current flowing in the at least two LED strings 132 and 134.

The control unit includes: a constant current control unit 220 controlling the operation of the DC-AC converter such that the current detected by the current detection unit maintains a constant current level; A burst input unit 204 for receiving the burst dimming signal; And an intermittent unit 205 for controlling the operation of the constant current controller according to the received burst dimming signal.

Here, the constant current control unit receives a current sensing voltage of the sensing resistor 192 to determine characteristics of switching signals (eg, frequency, duration, etc.) for the switching elements 112 and 114. I can regulate it.

Here, the intermittent unit 205 may include a photocoupler 250 for intermitting the control signal of the constant current controller 220 to be supplied to the DC-AC converter.

The constant current controller 220 supplies a switching control signal to the gate terminals of the switching elements 112 and 114 so that the DC-AC converter generates alternating current. The photocoupler 250 may be implemented such that the light receiving transistor element switches a path through which a switching control signal is supplied to the gate terminals of the switching elements 112 and 114.

The burst input unit 204 is a component for receiving a burst dimming signal, and includes an input transistor 241, an input resistor 244, a feedback resistor 243, a power supply voltage resistor 242, and an input terminal capacitor 245. It may include.

The intermittent unit 205 may include a shunt regulator 246 configured to receive a signal output from the burst input unit 204; A photocoupler 250 for transmitting the output signal of the shunt regulator 246 to the constant current controller 220; A bias resistor 248 and an input resistor 247 for the input terminal of the photocoupler 250 may be included.

Hereinafter, the operation of the illustrated LED driving circuit will be described.

The switching of the switching elements 112 and 114 creates a square wave power source, and the sine current flows to the primary side of the transformer unit 120 using the capacitor 118, and transfers energy to the secondary side of the transformer unit 120. do. In addition, the secondary sine current of the transformer unit 120 may balance the current flowing through the two LED strings 132 and 134 using the capacitors 176 and 178.

When the burst type dimming signal (Burst Signal) is generated to control the brightness of the LED light source device, the input transistor 241 is turned on during the active low, the reference of the shunt regulator (TL431) Since the voltage becomes equal to ground, the current of the photocoupler 250 does not flow, and the switching operation of the switching elements 112 and 114 is stopped.

That is, since burst dimming control is performed using a constant current controller (Power Controller IC) for constant current control without using an additional element for burst dimming control, there is a reduction in manufacturing cost / space.

Although the technical spirit of the present invention has been described in detail according to the above embodiment, it should be noted that the above embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

For example, for convenience of description, the above-described embodiment is described as an LED driving circuit for driving two LED strings, but the idea of the present invention can be easily applied to an LED driving circuit for driving three or more LED strings. In addition, of course, it belongs to the scope of the present invention.

1 is a circuit diagram showing a structure of an LED driving circuit for smoothing the driving power of LED strings in a linear driving method.

2 is a circuit diagram showing a structure of an LED driving circuit for smoothing the driving power of the LED strings in a switching manner.

3 is a block diagram showing the concept of an LED conversion circuit of an AC conversion method.

4 is a circuit diagram showing an LED driving circuit according to an embodiment of the present invention.

Claims (5)

delete delete LED strings; A DC-AC converter for converting DC power into AC power; A transformer unit configured to transfer the converted AC power; Rectifier for rectifying the AC power received from the transformer unit for supplying the LED string; A control unit controlling an operation of the DC-AC converter according to a burst dimming signal applied from the outside; And Current detecting means for detecting a current flowing in the LED string, The control unit, A constant current control unit controlling the operation of the DC-AC converter such that the current detected by the current detection unit maintains a constant current level; A burst input unit receiving the burst dimming signal; And An intermittent controlling the operation of the constant current controller according to the received burst dimming signal LED driving circuit comprising a. The method of claim 3, wherein The intermittent part, And a photocoupler for intermittently controlling the control signal of the constant current controller to be supplied to the DC-AC converter. The method of claim 3, wherein The intermittent part, LED drive circuit including a shunt regulator.

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